The adjuster screw on my front mech (bit that stops the chain going too far as I've probably named it wrongly) is stuck and the head is now pretty much threaded. Any suggestions for the best way to get it moving again? There is still some cross head on it but I need to work it loose somehow. It's attached to Shimano 105 flightdeck so it will I assume be shimano of some kind.
Assuming you are talking about one of the two limit screws (H and L) on your front derailleur, I would just spray a bit of penetrating oil (not WD40, but rather something like PB Blaster or Kroil) on it, let it "incubate" for an hour or two, then try a properly-sized Philips screwdriver and/or something like some needle-nosed pliers to turn the screw head.